At present, the pipeline robot is a new technology rising in recent years and combining fields of precision machinery, robotics, new material and control theory. A great many micro pipelines, such as heat transfer pipes for steam generators in nuclear power plant and industrial pipes and gas pipes in fields of metallurgy, oil, chemical, city heating supply and refrigeration, are used in modern industrial and agricultural productions and daily life. The poor work environment of these pipeline systems usually causes corrosion or fatigue failure to the pipes or makes potential internal pipeline faults develop into breakages, thus leading to leakage accidents. Therefore, the monitoring, diagnosis, clearing and maintenance of the pipelines has become the key to guarantee the security, smooth and efficient operation of the pipeline systems, and the in-serve and on-line pipeline detection has also become one of important directions of applications and developments of nondestructive inspection technology for pipeline. However, the operator cannot directly arrive at or be involved into the pipeline because of the local environment or the size limitation of the pipeline, thus, it is difficulty to maintain the pipeline.
With the rapid development of the pipeline robot both domestically and abroad, more and more pipeline maintenance work is performed by the pipeline robot. The moving mechanism is an important component of the pipeline robot. A pressure peristaltic inchworm type caterpillar device developed by Tokyo Institute of Technology has a slow speed and a complex control system. Another device is spiral driven type, such as a spiral driven circular pipeline robot disclosed in Chinese Patent No. 2007100500568, in which a driving wheel carrier is mounted on a shaft of a DC motor, three arm ends of the driving wheel carrier are hinged to a middle part of a driving wheel rod extending in a length direction of a body respectively, a driving wheel is mounted at an end part of the driving wheel rod, an included angle between an axis of rotation of the driving wheel and an axis of the body ranges from 3° to 30°, and a guide wheel carrier is mounted at a middle or front part of the body. The conventional spiral moving device generates an axial driving force to drive the robot forward by driving the driving carrier provided with a driving wheel to rotate and then driving the driving wheel mounted at the border of the driving carrier to spirally move along the inner wall of the pipeline by the driving carrier. Such structure has disadvantages of great energy loss and non-reliable transmission movement. The moving speed of the robot is affected by the value of the included angle between the axis of rotation of the driving wheel and the axis of the body. When the included angle is relatively smaller, the spiral angle of the spiral trail of the movement of the driving wheel is relatively smaller, the force driving the driving wheel to rotate is relatively larger, the rotation speed of the driving wheel is relatively quicker, and thus the robot moves smoothly. However, the spiral angle of the spiral trail is relatively smaller and the moving speed is relatively slower. With the increase of the included angle, the force driving the driving wheel to rotate gradually becomes small, the rotation speed of the driving wheel is reduced but the spiral angle of the spiral trail of the movement of the driving wheel is increased, and thus the moving speed of the robot may be gradually increased with the increase of the included angle. Beyond a certain value, however, the force driving the driving wheel to rotate is reduced to small, which leads to a further reduction of the rotation speed of the driving wheel and to a reduction of the moving speed of the robot. Besides, the operating stability of the robot is reduced and even the robot cannot move forward any more. Therefore, in terms of the conventional spiral moving device, the rotation speed of the driving wheel may change with the change of the included angle between the axis of rotation of the driving wheel and the axis of the body, thus leading to a poor operating stability of the device under different work conditions. In addition, since the driving wheel is turned to rotate by the driving wheel carrier, it is difficult to realize a precise position and a micro displacement adjustment for the robot, thus leading to a poor handling.